A vehicle seat having an arm rest that can be retracted into the seat back is known in the art. See JP2012-51492A, for instance. In the rear seat disclosed in this patent document, a pair of brackets are fixedly secured to the seat back frame, and a support shaft fixedly supporting an arm rest frame is pivotally supported by the brackets. Each bracket is formed with an arcuate slot centered around the pivot center, and a pair of guide pins projecting from the arm rest frame are fitted into the guide slots. The guide pins consist of two ends of a single rod extending laterally across the arm rest frame, and are received by the respective guide slots. The terminal ends of the guide slots define the deployed position and the retracted position of the arm rest, respectively. One of the guide pins is provided with frictional members frictionally engaging the surfaces of the brackets, respectively, as the arm rest frame pivots so that the arm rest may be retained at any desired angular position with respect to the seat back.
The brackets are each required to have a support hole for rotatably supporting the arm rest, and a guide slot for defining the angular range of the movement of the arm rest. Therefore, the size of each bracket is so significant that it may not be possible to attach the brackets to the respective side frames at a same elevation without interfering with other components of the seat back.
Furthermore, as the brackets are required to have a certain mechanical stiffness and strength, relatively stiff parts of the seat back frame are required to be selected for attaching the brackets. However, oftentimes, the side frames of the seat back have mutually different configurations, and may not have parts suitable for mounting the brackets at a same elevation. Therefore, one of the side frames may have to be reinforced solely for enabling the side frame to withstand the loading of the arm rest.